In a variety of applications, a coating can be applied to one or more surfaces of a component. The coatings can be made from any of a number of materials and can improve at least some of the surface properties of the component. In any coating process, it is usually important to achieve the design coating thickness. Too thin of a coating may not provide adequate protection; conversely, too thick of a coating may result in adherence problems between the coating itself and the underlying substrate due at least in part to a thermal expansion mismatch between the coating and the substrate.
Accordingly, a number of techniques have been developed for measuring the thickness of a coating applied to a component. For example, micrometers can be used to measure the distance between two points of contact between the micrometer and a component's surface. Another known method involves measuring variations in magnetic field or in impedance of Eddy current inducting coils caused by coating thickness variations. These methods can work in certain instances, but they lack the versatility to maintain their accuracy in connection with certain coatings processes and/or components with complex geometries such as fillets on a turbine engine blade or vane.
For instance, the accuracy of these and other known methods is dependent on the surface temperature of the component. As a result, these methods cannot be used until the component has cooled to ambient temperature or else the accuracy of the measurements is sacrificed. This delay may ultimately be counterproductive in manufacturing processes in which the coating is applied by thermal spray processes (e.g., high velocity oxygen fuel (HVOF), plasma, or arc spray) where the component is subjected to a large heat input. In such case, the component must cool to substantially ambient temperature so that an accurate thickness measurement can be made, but, if it is discovered that the coating thickness is below the design limits, then additional coating material must be added. However, extra coating material cannot simply be applied on top of the cooled coating material without diminishing the effectiveness of the coating's properties. Thus, the coating should be totally stripped and reapplied, which increases manufacturing cost and cycle time. Many of the prior systems do not allow for measurement of the coating thickness substantially simultaneously with the application of the coating itself.
Other factors that can affect the accuracy of measurement are surface curvature and the location of measurement relative to edges, holes or grooves. The difficulties associated with surface curvature can be solved by manufacturing special probes, which can significantly increase manufacturing costs. Thus, there is a need for a system that allows for the measurement of coating thickness substantially simultaneously with and/or immediately after completion of the coating process. Further, there is a need for a system in which the accuracy of measurement is not affected by component shape or surface temperature.